The invention discloses ultrasonic water immersion testing equipment for a metal square pipe. The equipment comprises a water tank body and a probe frame, wherein sliding rod seats are respectively arranged at two ends of the long side of the water tank body; a pair of sliding rods which are parallel with each other is connected between the two sliding rod seats. The probe frame is provided with a horizontal sliding seat; a vertical through hole is formed in the middle of the probe frame; the lower end of the probe frame is installed on a roller shaft 6 in a sliding manner; axial rollers are respectively installed at two ends of the roller shaft; the horizontal sliding seat is laid on the sliding rods through the axial rollers in the sliding manner; a pair of side seats is arranged at the top of the horizontal sliding seat; a probe clamp is rotatably installed between the two side seats; the probe clamp is hung above the through hole of the horizontal sliding seat; a vertically arranged dial is fixed on the inner wall of one side seat; a pointer matched with the dial is fixed on the side wall, facing the dial, of the probe clamp.